While riding through the countryside of Hyrule, the Triforce summons Link to Hyrule Castle, where he is sent to either Holodrum or Labrynna. He has a Triforce mark on his hand, which signifies him as a hero from Hyrule to the natives of those lands. Hyrule Historia reveals him to be the same hero from A Link to the Past, with the Oracle games being the journey he returns from that results in his boat being destroyed at the start of Link's Awakening.
Adorkable: Shown from some of his actions like botching a joke to nearly fainting at a kiss Zelda gives him.
Badass Adorable: This version of him gives even Toon Link a run for his money.
Beware the Nice Ones: He's generally portrayed as a friendly, kindhearted young man who tends to go out of his way to help those in distress. He is also the avatar of Courage, and has a history of beating the hell out of everything from dragons to demigods.
Rewarding Vandalism: Link's primary source of income is smashing random objects. Especially pottery.
You Are Too Late: Though he successfully saves the oracles and stops Veran and Onox, they succeed in their respective parts of Twinrova's plan.
Nayru, Oracle of Ages
Not to be confused with the goddess of wisdom, who goes by the same name, though this Nayru is more than likely a priestess of the other Nayru. She's a main character in The Legend of Zelda: Oracle of Ages and has the power to jump through time. She's well known for her beautiful singing voice in the kingdom of Labrynna and wields the Harp of Ages, which holds a part of her powers.
Expy: While many of the female characters in the Oracle games have sprites similar to Marin of Link's Awakening, given their use of the same graphic style, Nayru is especially similar, being a singer and harpist.
Not to be confused with the goddess of power, who goes by the same name, though this Din is more than likely a priestess of the other Din. She's a main character in The Legend of Zelda: Oracle of Seasons and holds the four seasons in their balance. She's a famous dancer in Holodrum and possesses the Rod of Seasons, which holds a part of her powers.
Weather Control Machine: The whole purpose of her existence. Enclose her in a crystal and watch the seasons go to hell.
Farore, Oracle of Secrets
Not to be confused with the goddess of courage, who goes by the same name, though this Farore is more than likely a priestess of the other Farore. She's a side character in both of the Oracle games. She resides in the Maku Tree that connects Labrynna and Holodrum, and Link must bring a secret he finds in one region to her so he can use new equipment in the other.
Demoted to Extra: There were initially going to be three Oracle games with her playing a large role in the third, but the developers decided it'd be too complicated to link three games so they made her the Oracle of Secrets instead.
The main villain of Oracle of Seasons, who actually resembles the regular enemy Iron Knuckle. He shows up to kidnap Din, the Oracle of Seasons, and throw the seasons in Holodrum for a loop. Later shown to be The Dragon to Twinrova.
Flat Character: They might both be Filler Villains, but at least Veran has the decency to show up sporadically throughout the game to somewhat flesh out her motivations. Onox doesn't reappear until it's time for the final battle.
Hijacked By Twinrova: Although if you're playing a Linked Game you'll know this even before you meet him.
Human Shield: He uses Din as one during the boss battle. Use the Rod of Seasons to gently knock her away to safety.
Large and in Charge: Definitely one of the more physically imposing villains Link's had to face.
Orcus on His Throne: Justified. As he's already imprisoned Din and sunken the Temple of Seasons, he doesn't need to do anything else to fulfill his part of Twinrova's plan, the world will tear itself apart just fine.
Shout-Out: The battle with his One-Winged Angel form is remarkably similar to Sigma's final form in the first Mega Man X game — he floats in the background and snaps his claws down at you, you ride them up high enough to strike the gem on his head. The game was developed by Capcom, so it's not surprising they'd throw in some kind of reference such as this.
Batman Gambit: Her method to inflict sadness on the people and light the Flame of Sorrow is to create an endless day and make the people of Labrynna labor endlessly to complete the Black Tower, creating a symbol of oppression that towers over the land.
Demonic Possession: Used three times - against Impa before the start of the game, Nayru early on, and later Queen Ambi. She tries to use it against Link after the first phase of her final battle with him, but he jumps out of the way.
She has a curious comment in the game about having possessed Ralph at one point, which only happens in the manga.
Xanatos Speed Chess: When Link successfully frees Nayru from her control, Veran possesses Queen Ambi instead. Though she not longer has free control over time, she's still in the past and in control of Labrynna since she's now their queen, so her work on the Black Tower can continue just fine.
The twin sisters Koume and Kotake, who were Ganon's adoptive parents in Ocarina of Time, are the true villains of the Oracle games. They intend on reviving their surrogate son with Princess Zelda's sacrifice.
Unexplained Recovery/Deader Than Dead: Word of God stated that the Oracle Games take place in the event that Ganon managed to kill Link during their final battle in Ocarina of Time, so how Twinrova managed to return from the dead is unknown. Likewise, assuming they are in fact still dead, their sacrificing themselves to ensure Ganon's resurrection makes them eligible for the Deader Than Dead trope.
The Final Boss of the game, whom Twinrova was trying to resurrect by sacrificing Zelda but since Link was able to stop the sacrifice from happening, Twinrova sacrificed herself instead. This made him return as a mindless killing monster instead of his usual intelligent self.
Almighty Idiot: He was revived to be as powerful as he ever was, but with none of his intelligence form before.
Bigger Bad: He's not directly involved in the plot, staying a dead body for most of the game. The real Big Bads of the linked game are his surrogate mothers, and the plot is driven by them trying to resurrect him.
Dying as Yourself: It is implied from Ganon's final words after being vanquished by Link ("Gwa Ha Ha! I am the Evil King Ganon...!") that he at least regained some clarity of who he is upon the final blow.
What Could Have Been: Concept art included in the Hyrule Historia indicated that Ganondorf, Ganon's human form, would have appeared in the game, implying that Link failed to save Zelda from being sacrificed.
An obnoxious young man first seen as Nayru's bodyguard. When the Oracle is kidnapped by Veran, he goes tearing off after them, screaming for Nayru. He occasionally shows up to give Link hints, usually nagging him for stopping to help others instead of rescuing Nayru.
"I couldn't tell if it was a man or a woman! It was scary!"
Camp Straight: He's pretty fabulous in his flares with purple trim, flippy hair, hip-accenting pose, and (look closely) green nail polish. But he spends most of his screen time worrying about Nayru, and the manga makes it clear that his interest in her is romantic.
Grandmother Paradox: As Queen Ambi's eventual descendant, he would cease to exist if Ambi was harmed or killed. During his confrontation with Veran (possessing Ambi's body), he acknowledges this and resolves to fight her anyway. He then gets pwned.
Heroic Sacrifice: Just narrowly subverted. Although he acknowledges that killing Ambi, his ancestor, will result in his existence being erased, he decides to go through with it anyway just to save Nayru and Labrynna from Veran. Veran-as-Ambi proceeds to kick his ass and leave him incapacitated, but alive.
Expy: Of Tarin from Link's Awakening and by extension, of Mario. It seems he gets more Mario like with each successive game. In Link's Awakening, Tarin's sprite looked a lot like Mario, but his character art was somewhat different. In Ocarina of Time he has the blue overalls and red shirt. In Oracle of Seasons, he has Mario's "M" logo on his hat, Mario's exact mustache, sideburns, nose, ears, and eyes. He even gives Link a mushroom as part of the trading sequence.
Granddaughter of Syrup, the witch who sells you potions in the previous games. She appears after you defeat a certain number of enemies, triggering a sort of mini-game where you bump into each other and lose some of your items. You then have to race with her to collect each other's items.
Ascended Extra: She plays a large role in the Oracle of Seasons manga.
Well Done Granddaughter Gal: It's implied by something she says after giving her the Touching Book that she just wants Syrup to appreciate her.
The Princess of Hyrule, she sends Link to Labrynna and Holodrum to aid the endangered oracles. The joined game reveals that the true aim of Koume and Kotake is to sacrifice her in order to resurrect Ganondorf. She is apparently the same princess from A Link to the Past.
Continuity Snarl: Word of God and All There in the Manual says this is the same Zelda from A Link to the Past (and also the same Link), but when she is introduced Oracle of Seasons her lines imply that they are meeting for the first time. Her lines have the correct phrasing in Oracle of Ages.
Demoted to Extra: Kind of. She's really only seen in the joined game, although the manga indicates that she's the one who sends Link to the aid of Din and Nayru.